"At the GNOME Developer Experience Hackfest in Brussels, the GNOME developer community has tackled the problem of specifying a canonical development language for writing applications for the GNOME desktop. According to a blog post by Collabora engineer and GNOME developer Travis Reitter, members of the GNOME team are often asked what tools should be used when writing an application for the desktop environment and, up until now, there has been no definitive answer. The team has now apparently decided to standardise on JavaScript for user-facing applications while still recommending C as the language to write system libraries in." Discuss.

Back in the day, Gnome started using Clutter bindings to implement Gnome 3. I'm not aware of them switching from Gtk to Clutter for app development, that would be even bigger news.

Clutter has nothing to do with it. Gnome has supported application coding in JS for quite a few years now, via the 'seed' (WebKit) or 'gjs' (Mozilla) engines. Several of the games in the later Gnome 2.x releases were written in JS, with gtk widgets, and (I think) some embedded clutter stuff for the game itself.